TEMPEST-D is a CubeSat project of
CSU (Colorado State University) Fort Collins, CO, with the objective to
demonstrate the ability to monitor the atmosphere with small
satellites. The team will demonstrate a radiometer aboard a 6U CubeSat
(30 cm x 20 cm x 10 cm) and subsequently plan to deploy a constellation
of satellites to study cloud processes. The team, led by Steven Reising
(PI), professor of electrical and computer engineering, is developing
instrumentation for CubeSats that can observe, in real time, a storm as
it grows and progresses. 1)

TEMPEST-D will reduce the risk, cost
and development time of a future constellation of 6U-Class
nanosatellites to directly observe the time evolution of clouds and
study the conditions that control the transition from non-precipitating
to precipitating clouds using high-temporal resolution observations.
TEMPEST-D provides passive millimeter-wave observations using a compact
radiometer (90-183 GHz) that fits well within the size, weight and
power (SWaP) requirements of the 6U-Class satellite architecture.
TEMPEST-D is suitable for launch through NASA’s CSLI (CubeSat
Launch Initiative), for which it was selected in February 2015. 2)3)

By measuring the temporal evolution
of clouds from the moment of the onset of precipitation, a TEMPEST
constellation mission would improve our understanding of cloud
processes and help to constrain one of the largest sources of
uncertainty in climate models. Knowledge of clouds, cloud processes and
precipitation is essential to our understanding of climate change.
Uncertainties in the representation of key processes that govern the
formation and dissipation of clouds and, in turn, control the global
water and energy budgets lead to substantially different predictions of
future climate in current models.

The goal of the TEMPEST-D is a
mission to validate the performance of a CubeSat microwave radiometer
designed to study precipitation events on a global scale. The TEMPEST
constellation of 6U CubeSats is designed to sample convective
precipitation events, from cloud formation, through ice formation and
precipitation to cloud dissipation. 4)

The TEMPEST-D project is to increase
the TRL (Technology Readiness Level) of the millimeterwave radiometer
instrument from 6 to 9. 5)

The TEMPEST-D mission success criteria for a 90-day mission after on-orbit commissioning are as follows:

1) To demonstrate feasibility of
differential drag measurements required to achieve the desired time
separation of 6U-Class satellites deployed together in the same orbital
plane.

2) To demonstrate cross-calibration
with 2 K precision and 4 K accuracy between TEMPEST-D millimeter-wave
radiometers and the NASA/JAXA GPM/GMI or the Microwave Humidity Sounder
currently in orbit on two NOAA satellites and two ESA/EUMETSAT
satellites.

Spacecraft:

TEMPEST-D 1 is a partnership among
CSU, JPL and spacecraft provider BCT (Blue Canyon Technologies Inc.) of
Boulder, CO. BCT has recently been awarded a contract to build, test,
and operate a new 6U-class satellite. BCT will deliver the 6U
spacecraft, ready for instrumentation, for the TEMPEST-D project, led
by CSU (Colorado State University), Fort Collins, CO. TEMPEST-D is
supported by NASA’s Science Mission Directorate, Earth Science
Division and is managed by NASA’s ESTO (Earth Science Technology
Office). NASA/JPL(Jet Propulsion Laboratory) will provide the
five-channel millimeter-wave radiometer instrument. 6)

BCT will
integrate the TEMPEST-D payload with the 6U spacecraft bus and perform
environmental testing of the complete spacecraft. The spacecraft will
be operated from BCT’s Mission Operations Center in Boulder,
Colorado. BCT’s 6U spacecraft is a high-performance CubeSat that
includes an ultra-precise attitude control system that allows for
accurate knowledge and fine-pointing of the satellite payload.

Launch: The TEMPEST-D CubeSat
was launched to the ISS on 21 May 2018 (08:44 UTC) on ELaNa 23 of NASA.
The launch vehicle was the Antares 230 with Cygnus CRS OA-9E, also
known as Orbital Sciences CRS Flight 9E, the tenth planned flight of
the Orbital ATK unmanned resupply spacecraft Cygnus. The launch site
was MARS (Mid-Atlantic Regional Spaceport), Wallops Island, VA, USA. 8)9)

• AeroCube-12A and -12B, a pair
of 3U CubeSats of the Aerospace Corporation, El Segundo , CA, to
demonstrate a the technological capability of new star-tracker imaging,
a variety of nanotechnology payloads, advanced solar cells, and an
electric propulsion system on on one of the two satellites (AC12-B).

• EnduroSat One, a 1U CubeSat
of Bulgaria, developed by Space Challenges program and EnduroSat
collaborating with the Bulgarian Federation of Radio Amateurs (BFRA)
for the first Bulgarian Amateur Radio CubeSat mission.

• September 4, 2019: A new view
of Hurricane Dorian shows the layers of the storm, as seen by an
experimental NASA weather satellite that's the size of a cereal box.
TEMPEST-D reveals rain bands in four layers of the storm as Hurricane
Dorian approaches Florida on Sept. 3, 2019. The multiple vertical
layers show where the strongest convective "storms" within the
hurricane are pushing high into the atmosphere, with pink, red and
yellow corresponding to the areas of heaviest rainfall. 11)

Figure 4: Hurricane Dorian off
the coast of Florida, as seen by the small satellite TEMPEST-D at 2
a.m. EDT on Sept. 3, 2019 (11 p.m PDT on Sept. 2, 2019). The layers in
the animation reveal slices of the hurricane from four depths, taken at
different radio wavelengths. The vertical view of Dorian highlights
where the storm is strongest in the atmosphere. The colors in the
animation show the heavy rainfall and moisture inside the storm. The
least-intense areas of rainfall are shown in green, while the most
intense are yellow, red and pink (image credit: NASA/JPL-Caltech)

- Known as a CubeSat,
TEMPEST-D (Temporal Experiment for Storms and Tropical Systems
Demonstration) uses a miniaturized version of a microwave radiometer -
a radio wave instrument used to measure rain and moisture within the
clouds. If TEMPEST-D can successfully track storms like Dorian, the
technology demonstration could lead to a train of small satellites that
work together to track storms around the world. CubeSats are much less
expensive to produce than traditional satellites; in multiples they
could improve our global storm coverage and forecasting data.

- TEMPEST-D is led by Colorado
State University in Fort Collins and managed by JPL in partnership with
Blue Canyon Technologies in Boulder, Colorado, and Wallops Flight
Facility in Virginia. The mission is sponsored by NASA's Earth Ventures
program and managed by the Earth Science Technology Office at NASA
Headquarters in Washington. The radiometer instrument was built by JPL
and employs high-frequency microwave amplifier technology developed by
Northrop Grumman.

• September 3, 2019: The
Advanced Rapid Imaging and Analysis (ARIA) team at NASA's Jet
Propulsion Laboratory in Pasadena, California, created this flood map
(Figure 5) depicting areas of the Bahamas that are likely flooded (shown by light blue pixels) as a result of Hurricane Dorian. 12)

Figure 5:
The map was derived from synthetic aperture radar (SAR) data acquired
on 2 September 2019, by the Copernicus Sentinel-1 satellites operated
by the European Space Agency (ESA). The map covers an area of 176 km by
170 km shown by the large red polygon. Each pixel measures about 30 m
across. This map can be used as guidance to identify areas that are
likely flooded, and may be less reliable over urban and vegetated areas
(image credit: NASA/JPL-Caltech/ARIA Team)

• August 29, 2019: Several
instruments and spacecraft from NASA's Jet Propulsion Laboratory in
Pasadena, California, have eyes on Hurricane Dorian, capturing
different types of data from the storm. 13)

Figure 6: Three images of
Hurricane Dorian, as seen by a trio of NASA's Earth-observing
satellites on 27-29 August 2019. Left: image of the MM instrument on
the 6U CubeSat TEMPEST-D; Center: image of AIRS on Aqua satellite;
Right: image of the CloudSat satellite. The data sent by the spacecraft
revealed in-depth views of the storm, including detailed heavy rain,
cloud height and wind (image credit: NASA/JPL-Caltech)

- The weather-observing satellite
TEMPEST-D captured imagery of Hurricane Dorian off the coast of Puerto
Rico in the early morning hours (local time) of Aug. 28, 2019. At a
vantage point of400 km above the storm, the CubeSat used its
miniaturized radio-wave-based instrument to see through the clouds,
revealing areas with heavy rain and moisture being pulled into the
storm.

- TEMPEST-D is a
technology-demonstration mission led by Colorado State University and
managed by JPL in partnership with Blue Canyon Technologies and Wallops
Flight Facility in Virginia. The mission is sponsored by NASA's Earth
Ventures program and managed by the Earth Science Technology Office.
The radiometer instrument was built by JPL and employs high-frequency
microwave amplifier technology developed by Northrop Grumman.

Figure 7: Hurricane Dorian off
the coast of Puerto Rico, as seen by the small satellite TEMPEST-D on
Aug 28, 2019 (local time). The colors in the image reveal the heavy
rain and moisture inside the storm. The least intense areas of rainfall
are shown in green and most intense are yellow and pink (image credit:
NASA/JPL-Caltech)

- The AIRS instrument aboard the
Aqua satellite senses emitted infrared and microwave radiation from
Earth. The information is used to map such atmospheric phenomena as
temperature, humidity, and cloud amounts and heights. In Figure 8,
the large purple area indicates very cold clouds carried high into the
atmosphere by deep thunderstorms. These clouds are also associated with
heavy rainfall. Blue and green indicate warmer areas with shallower
rain clouds, while the orange and red areas represent mostly cloud-free
air.

- AIRS, in conjunction with the
Advanced Microwave Sounding Unit (AMSU), provides a 3D look at Earth's
weather and climate. Launched into Earth orbit in 2002, the AIRS and
AMSU instruments are managed by JPL under contract to NASA.

Figure 8:
An infrared image of Hurricane Dorian, as seen by the AIRS instrument
aboard NASA's Aqua satellite at 1:30 p.m. EDT (10:30 a.m. PDT) on 29
August 2019. The large purple areas are cold clouds, carried high into
the atmosphere by deep thunderstorms. Blue and green show warmer areas
with less rain clouds, while orange and red represent mostly cloud-free
air (image credit: NASA/JPL-Caltech)

- NASA's CloudSat satellite
provided a 3D animation after passing over Dorian, still a tropical
storm at the time, near Puerto Rico. CloudSat uses an advanced
cloud-profiling radar that "slices" through clouds, enabling us to see
their height, their different layers and the areas where the heavier
bands of rain are found within the storm system.

• July 30, 2019: TEMPEST-D
(Temporal Experiment for Storms and Tropical
Systems—Demonstration), a 6U CubeSat, is still providing precise
images of global weather—exceeding the expectations of even its
engineers. 14)

- TEMPEST-D is about the size of an
Oxford dictionary and was deployed from the International Space Station
last July carrying a miniaturized microwave radiometer. Measuring at
five frequencies, TEMPEST-D can see through clouds to reveal the
interior of storms where raindrops and ice crystals form.

- The project is led by principal
investigator Steven Reising, professor of electrical and computer
engineering, whose team developed the satellite supported by an $8.2
million grant from NASA's Earth Science Technology Office.

- "TEMPEST-D is the first weather
satellite on a CubeSat to image the interior of storms on a global
basis," said Reising, who heads the project in collaboration with
co-investigator V. "Chandra" Chandrasekar, University Distinguished
Professor in electrical and computer engineering. "We have shown that
the quality of our data is at least as high as that from large
operational radiometers in orbit."

- Chandra is a veteran of multiple
large weather satellite missions. "This mission has been wildly
successful—beyond our dreams," he said. "It was just supposed to
demonstrate the technology of the radiometer and orbital maneuvers.
Then it started taking data, and people were saying, "Wow!".... It's
looking at hurricanes and producing very high-quality global
data—very much like a big mission."

Figure 9: Steven Reising,
professor of electrical and computer engineering, holds a model of the
TEMPEST-D satellite. After meeting all its benchmarks for demonstrating
small-satellite weather forecasting capabilities during its first 90
days, a Colorado State University experimental satellite is operating
after more than one year in low-Earth orbit (image credit: Bill Cotton)

Demonstrating future technologies

- TEMPEST-D is intended as a
proof-of-concept for next-generation Earth-observing technologies that
are orders of magnitude smaller and lower cost than traditional
satellites operated by federal agencies.

Figure 10: TEMPEST-D data from
Jan. 29, 2019, shows a storm in the southeastern U.S., with
ground-based weather radar rainfall estimates in the lower right panel.
The areas covered by each radar are represented by circles (image
credit: V. Chandrasekar)

- The ultimate goal is to send not
just one but a constellation of six to eight CubeSats like TEMPEST-D
into space. The satellites would fly in a train, watching storms
develop every few minutes. Such fine temporal resolution would offer
unprecedented views inside storms—such as those that threaten the
Atlantic Basin and the eastern U.S. every year—to monitor how
they develop every few minutes over a 30-minute period. Such a mission
could also improve scientists' understanding of cloud processes and the
influence of surrounding water vapor.

- Christian Kummerow, director of
CSU's Cooperative Institute for Research in the Atmosphere, is also a
co-investigator on TEMPEST-D. He worked with Reising to develop new
techniques to retrieve cloud and precipitation information of interest
to atmospheric scientists.

- NASA mission: TEMPEST-D is led by
CSU and managed by NASA's Jet Propulsion Laboratory (JPL) in Pasadena,
California, in partnership with Boulder-based Blue Canyon Technologies.
The ground station is operated by NASA Wallops Flight Facility in
Virginia. The mission is sponsored by NASA's Earth Ventures program and
managed by the Earth Science Technology Office. The radiometer
instrument was built by JPL and employs extremely high-frequency
microwave amplifier technology developed by the Northrop Grumman
Corporation.

• September 20, 2018: TEMPEST-D
took its first images of Hurricane Florence on 11 September, just hours
after its instrument was turned on. The 6U CubeSat carries a
state-of-the-art miniaturized microwave radiometer, an instrument that
sees through the thick clouds to reveal the hidden interior of storms. 15)

Figure 11: This animation
combines the TEMPEST-D data with a visual image of the storm from
NOAA's GOES (Geoweather Operational Environmental Satellite) weather
satellite. The brightly colored image taken by the small, experimental
satellite TEMPEST-D captures Hurricane Florence over the Atlantic
Ocean. The colors reveal the eye of the storm, surrounded by heavy
rain. The green areas highlight the extent of the rain being produced
by the storm, with the most intense rain shown in the yellow and red
areas. The TEMPEST-D data is contrasted with a visible image of
Florence taken by the GOES weather satellite, which shows the familiar
cyclone-shaped clouds of the storm, but doesn't reveal what's inside
(image credit: NASA/NOAA/Naval Research Laboratory Monterey/JPL-Caltech)

- The image taken by TEMPEST-D
captures Florence over the Atlantic Ocean, revealing the eye of the
storm surrounded by towering, intense rain bands. The green areas
highlight the extent of the rain being produced by the storm, with the
most intense rain shown in yellow and red. The TEMPEST-D data is
contrasted with a visible image of Florence that shows the familiar
cyclone-shaped clouds of the storm but doesn't reveal what's inside.

- TEMPEST-D's mission is to test
new, low-cost technology that could be used in the future to gather
more weather data and help researchers better understand storms. The
level of detail in the small-satellite image is similar to what
existing weather satellites produce.

- "We were challenged to fit this
instrument into such a small satellite without compromising data
quality and were delighted to see it work right out of the box," said
Sharmila Padmanabhan, who led the instrument development at NASA's Jet
Propulsion Laboratory in Pasadena, California.

- Shrinking weather satellites
could one day help scientists provide more frequent updates on
developing storms. "TEMPEST-D paves the way for future missions where
we can afford to fly many of these miniaturized weather satellites in
constellations. Such a deployment would enable us to watch storms as
they grow," said Steven Reising, the principal investigator for
TEMPEST-D at Colorado State University.

- TEMPEST-D is a
technology-demonstration mission led by Colorado State University and
managed by NASA/JPL, in partnership with Blue Canyon Technologies and
Wallops Flight Facility, Virginia. The mission is sponsored by NASA's
Earth Ventures program and managed by the Earth Science Technology
Office. The radiometer instrument was built by JPL and employs
high-frequency microwave amplifier technology developed by Northrop
Grumman Corporation.

• July 13, 2018: NanoRacks
successfully completed the 14th CubeSat Deployment mission from the
Company’s commercially developed platform on the International
Space Station. Having released nine CubeSats into low-Earth orbit, this
mission marks NanoRacks’ 185th CubeSat released from the Space
Station, and 217th small satellite deployed by NanoRacks overall. 16)

- The CubeSats deployed were
launched to the Space Station on the ninth contracted resupply mission
for Orbital ATK (now Northrop Grumman Innovation Systems) from Wallops
Island, Virginia in May 2018.

- NanoRacks offered an affordable
launch opportunity, payload manifesting, full safety reviews with NASA,
and managed on-orbit operations in order to provide an end-to-end
solution that met all customer needs.

- The CubeSats mounted externally
to the Cygnus spacecraft from the May 2018 launch are scheduled to be
deployed on Sunday, July 15th, pending nominal operations.

Sensor complement: (MM Radiometer)

MM Radiometer (Millimeter-wave Radiometer)

The MM radiometer is being built by
NASA/JPL and performs continuous measurements at five frequencies, 89,
165, 176, 180 and 182 GHz. The five-frequency radiometer is based on
the direct-detection architecture, in which the RF input to the feed
horn is amplified, bandlimited, and detected using Schottky diode
detectors. 17)
The use of direct-detection receivers based on InP HEMT MMIC LNA front
ends substantially reduces the mass, volume and power requirements of
these radiometers. 18)
Input signals are bandlimited using waveguide-based bandpass filters to
meet the radiometer bandwidth requirements of 4±1 GHz at center
frequencies of 89 and 165 GHz, as well as 2±0.5 GHz at 176, 180
and 182 GHz center frequencies (Ref. 5).

The TEMPEST-D
instrument design is based on a 165 GHz to 182 GHz radiometer design
inherited from RACE and an 89 GHz receiver developed under the ESTO
ACT-08 and IIP-10 programs at CSU (Colorado State University) and JPL.
All receivers were jointly developed by JPL and the Northrop Grumman
Corporation. The TEMPEST reflector scanning and calibration methodology
has been adapted from the ATMS (Advanced Technology Microwave Sounder).
This methodology has been validated on the Global Hawk unmanned aerial
vehicle (UAV) using the HAMSR (High Altitude MMIC Sounding Radiometer)
instrument. 19)

The TEMPEST-D instrument occupies a
volume of 3U (normally defined as 34 cm x 10 cm x 10 cm) and is
designed for deployment in a 6U CubeSat. The instrument is mounted on a
temperature controlled bench that interfaces with the spacecraft
structure using thermally isolating spacers. Figure 13 shows the mechanical layout of the instrument components on the instrument bench.

The TEMPEST-D radiometer performs
cross-track scanning, measuring the Earth scene between ±45°
nadir angles, providing an 825 km wide swath from a 400 km nominal
orbit altitude. Each radiometer pixel is sampled for 5 ms. The
radiometer performs end-to-end calibration during each rotation of the
scanning reflector. The radiometer observes both cosmic background
radiation at 2.7 K and an ambient blackbody calibration target (at
approximately 300 K) every 2 seconds, for a scan rate of 30 RPM. A
schematic representation of the TEMPEST-D observing profile over a
360° reflector scan and the resulting output data time series are
shown in Figure 14.

The TEMPEST-D flight model
radiometer instruments (two copies, FM1 and FM2) have been designed,
fabricated and integrated at JPL. Figure 15
shows the TEMPEST-D instrument, including scanning reflector (top
left), dual-frequency feed horn, originally developed under a NASA ESTO
Advanced Component Technology (ACT-08) program (center left), and the
four radiometer channels from 165 to 182 GHz, including front-ends,
power divider, bandpass filter bank and detectors. Measurements of the
receiver bandpass and linearity of each of the five frequency channels
have been performed at JPL.

Both TEMPEST-D flight model
instruments have been integrated with the XB1 6U spacecraft avionics
and bus at BCT, as shown in Figure 16.
The TEMPEST-D flight model radiometer and spacecraft bus have passed
electromagnetic self-compatibility tests in an anechoic chamber
designed for EMI (Electromagnetic Interference)testing.

The information compiled and edited in this article was provided byHerbert
J. Kramer from his documentation of: ”Observation of the Earth
and Its Environment: Survey of Missions and Sensors” (Springer
Verlag) as well as many other sources after the publication of the 4th
edition in 2002. - Comments and corrections to this article are always
welcome for further updates (herb.kramer@gmx.net).